This invention relates to thread roll attachments for screw thread machines and the like, and more particularly to attachments having improved means for releasably and adjustably mounting thread rolls on the attachments. More specifically, this invention relates to an improved method and means for rolling tapered pipe threads onto stock, and for manually adjusting the rotational axes of its thread rolls.
The U.S. Pat. No. 4,617,816, which is owned by the same company to which this application has been assigned, discloses a thread rolling attachment of the type with which this invention is generally concerned. An attachment of the type disclosed in the above-noted patent includes a pair of thread roll supporting arms, which are pivotally mounted intermediate their ends on a yoke, to be forced into rolling engagement with the opposite sides of a piece of rotating bar stock in order to form threads in the stock. The arms are actuated by a wedge element which is manipulated by a fluid pressure operated piston.
Typically, thread rolls are bound to supporting arms which place the rotational axes of the thread rolls parallel to and within the same plane as the longitudinal axis of the stock. This arrangement proves to be inadequate when tapered stock surfaces are encountered, because a similarly tapered thread roll must be employed in order to maintain the parallel axes. It has heretofore been customary to match the diametrally larger end of the thread roll to the diametrally smaller end of the stock and vice versa. This method however, is plagued by slippage occurring between the stock and thread roll caused by a variation of the rotational velocity along the length of the working surfaces of the thread rolls. Such slippage reduces the quality of threads produced upon the tapered stock surface.
Accordingly, it is an object of this invention to provide a novel thread roll attachment for producing high quality threads on a circumferentially tapered peripheral stock surface.
Another object of this invention is to provide an improved attachment of the type described which enables both the quick removal of its associated thread rolls, and the adjustment of the axes of the rolls.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.